Add slot field to inventoryManager.getItemInHand

[zyxkad]

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• Please check if the PR fulfills these requirements

• The commit message are well described
• Docs have been added / updated (for features or maybe bugs which were noted). If not, please update the needed documentation here. This is not mandatory
• All changes have fully been tested

• What kind of change does this PR introduce? (Bug fix, feature, ...)
  Feature

• What is the current behavior? (You can also link to an open issue here)
  The getItemInHand method will not return the slot info

• What is the new behavior (if this is a feature change)?
  Now it will

• Does this PR introduce a breaking change? (What changes might users need to make in their scripts due to this PR?)
  Yes, the player have to check nil now instead of {} for empty item
  And the slots are begin with 1 now

• Other information:

  • Add slot info for inventoryManager.getItemInHand Advanced-Peripherals-Features#67
  • Slot indices are 0-based instead of 1-based #587

close IntelligenceModding/Advanced-Peripherals-Features#67